The present invention relates generally to the packaging of integrated circuits (ICs). More particularly, a variety of leadframe designs suitable for use in packaging IC dice are described that facilitate stress reduction in and around an attached die.
There are a number of conventional processes for packaging integrated circuit (IC) dice. By way of example, many IC packages utilize a metallic leadframe. The leadframe typically includes a plurality of leads or contacts, and optionally a die attach pad (paddle) upon which a die may be physically attached by means of a suitable adhesive material. The die is typically electrically connected to the leadframe leads by appropriate connectors such as bonding wires. In general, the die and portions of the leadframe are encapsulated with a molding material to protect the electrical connections and the delicate electrical components on the active side of the die.
During testing and operation, packages may be repeatedly exposed to temperature cycling and other environmental stresses. By way of example, some testing protocols require cycling between temperatures as high as 125° C. and as low as −40° C. Such extreme changes in temperature may lead to delamination of the die from the die attach pad, which in turn may cause poor thermal performance, die cracking, the shearing of wirebonds attached to the die pad and other problems.
FIGS. 1A and 1B illustrate diagrammatic side and top views of a die 103 mounted on a conventional die attach pad 105. Adhesive 109 secures the die 103 to the conventional die attach pad 105. The depth Z of adhesive 109 between die attach pad 105 and die 103 is relatively constant across the bottom surface of die 103. As seen in FIGS. 1A and 1B standard die attach pads 105 tend to have a rectangular shape, a relatively smooth top surface without recesses, and sharp corners 110.
FIG. 1C illustrates a diagrammatic side view of a package 119 that incorporates die 103 and die attach pad 105. Bonding wires 113 electrically connect die 103 to surface 107 of die attach pad 105. Molding material 117 encapsulates die 103 and die attach pad 105.
As noted earlier, the testing and operation of a package can damage the integrity of the package. Stresses tend to concentrate in sharp corners, such as corners 110 of FIG. 1B. Stresses may also concentrate on edges. Such stresses may result in delamination or cracking. The crack front may propagate, for example, from corner 110 of FIG. 1B into the interior of die attach pad 105, causing die attach pad 105 and die 103 to shift relative to one another. In package 119 of FIG. 1C, such cracking may cause die attach pad 105 and molding material 117 to shift relative to one another.
The shifting of die attach pad 105 relative to molding material 117 of FIG. 1C may cause a number of problems. Such shifting may cause bonding wires 113 to be disengaged from surfaces 107. Additionally, delamination between layers of the package may create air gaps within the package. Air gaps tend to reduce the thermal performance of package 119.
In view of the foregoing, there are continuing efforts to reduce stresses and to provide structures that reduce the probability of die delamination and other damage in IC packages.